In a general color automatic determining method used in an image processing apparatus, monochrome/color determination (hereinafter, described as color determination) is performed in pixel units to a document which has been read. The color determination of a document is performed by an integrated value of the number of pixels determined as color.
For example, in Japanese Patent Application Laid-Open Publication No. 2001-036752, there is disclosed an image processing apparatus which performs color determination once again to a pixel which has been determined that it is chromatic (color). That is, the number of pixel groups in which a predetermined number of pixels determined to be a color pixel continue in the horizontal scan line and the number of times that such pixel groups continue in the vertical scanning direction by a predetermined number of times are counted, and then it is determined finally whether a document is a color document or a monochrome document based on these values.
Japanese Patent Application Laid-Open Publication No. 2007-116419 discloses an image processing apparatus which makes the influence of a color shift which occurs at the time of reading a document on color determination small by performing down-scaling processing to image data.
In the color automatic determining method mentioned above, color determination of a document is performed by performing color determination about each pixel, and then counting the number of pixels determined to be a color pixel. At that time, because substantial color determination processing is performed only in the first color determination, when noise or the like is included in read image data, such pixels might be falsely determined to be a color pixel. Accordingly, there is a problem that a case where a monochrome pixel is determined as a color pixel occurs and thus the determination accuracy of color determination declines.
Further, although various actions such as edge detection processing and foundation removal processing are taken in order to improve the color determination accuracy, such processing causes increase of processing procedures in color determining processing, and thus processing time becomes long.
In addition, about hardware for performing processing such as edge detection processing and foundation removal processing, there is a problem that a circuit and a structure are complicated and large in scale.